Well even if the PS4 pops 150 million the Xbox One does 80 million and the Wii U does 30 million (really optimistic predictions) that's still only a total of 260 million units, which is still less than what we currently have.
The problem too is I can't really see the Wii U managing 30 (more around 20 millionish) and the Xbox One 80, I have no way of knowing but I can't see it happening. So for now realistically speaking it's safe to assume there will be a decline.







